Kinematics of the knee after unicompartmental arthroplasty is not the same as normal and is similar to the kinematics of the knee with osteoarthritis.

PURPOSE: It is common to assert that restoration of normal knee kinematics is essential for the best functional result after knee arthroplasty. Previous studies using the progression of the geometric centre axis have suggested that kinematics after unicompartmental arthroplasty is markedly different from the normal. For this study, the transepicondylar axis was used because this axis is closer to the flexion axis and should be a better reference for motion. The following hypothesis was tested: the transepicondylar axis would again show that the postoperative kinematics does not restore normal motion and is closer to that before replacement. METHODS: Seventeen osteoarthritic knees were tested before and after unicompartmental arthroplasty using a three-dimensional to two-dimensional registration technique tracking the transepicondylar axis to calculate translation and rotation of this axis. Results were compared for the seventeen knees before and after arthroplasty and were compared to the normal knee as measured in our previous study. RESULTS: Similar motion patterns in the pre- and postoperative knees were shown but both the pre- and postoperative motion were markedly different from the normal knee. CONCLUSIONS: This result supported our hypothesis. The clinical relevance is that medial unicompartmental arthroplasty cannot restore the motion of the knee to normal in the living knee. Therefore, it would be expected that the patient for unicompartmental knee might not feel normal. It may not be possible depending on ligaments alone to restore the knee to normal, and the changes in the articular shapes and the surgical procedure may also be necessary.

Metal block augmentation for bone defects of the medial tibia during primary total knee arthroplasty.

BACKGROUND: Stable and well-aligned placement of tibial components during primary total knee arthroplasty is challenging in patients with bone defects. Although rectangular block-shaped augmentations are widely used to reduce the shearing force between the tibial tray and bone compared with wedge-shaped augmentations, the clinical result remains unclear. This study aimed to evaluate the outcome of primary total knee arthroplasty with metal block augmentation. METHODS: We retrospectively reviewed the 3- to 6-year follow-up results of 33 knees that underwent total knee arthroplasty with metal block augmentation (metal-augmented group) for bone defects of the medial tibia and 132 varus knees without bone defects as the control group. All surgeries were performed using posterior-stabilized cemented prostheses in both groups. Cemented stems were routinely augmented when the metal block was used. RESULTS: There were no differences in implant survival rates (100% in metal-augmented and 99.2% in control) or knee function scores (82 points in metal-augmented and 84 points in control) between the two groups at the final follow-up examination (P = 0.60 and P = 0.09, respectively). No subsidence or loosening of the tibial tray was observed. Of 33 metal-augmented total knee arthroplasties, a nonprogressive radiolucent line beneath the metal was detected in 10 knees (30.3%), and rounding of the medial edge of the tibia was observed in 17 knees (51.5%). CONCLUSIONS: The clinical results of total knee arthroplasty with metal augmentation were not inferior to those in patients without bone defects. However, radiolucent lines were observed in 30.3%.

Uncemented third-generation ceramic-on-ceramic total hip arthroplasty using metal acetabular shell with direct taper locking liner.

BACKGROUND: The ceramic-on-ceramic (CoC)-bearing couple in total hip arthroplasty (THA) was developed to reduce the wear debris and osteolysis. Although the mechanical strength of third-generation ceramic has improved over previous generations, the risk of osteolysis and ceramic fracture is still an important concern. METHODS: We studied 124 uncemented THAs with third-generation CoC-bearing couple implanted between 2000 and 2004. The ceramic liner and head were secured with the direct taper locking mechanism. One hundred and eleven hips were followed-up for minimum of 8 years, with an average follow-up period of 10.1 years (range 8.0-12.8 years). Patients were evaluated with a particular emphasis on the prevalence of the osteolysis and the ceramic fracture. RESULTS: The survivorship with the end point as implant revision for any reason was 94.9 % (95 % confidence intervals 90.0-99.3 %) at 12.8 years. Revisions were performed because of one ceramic liner fracture, three dislocations, and two deep infections. No radiographic evidence of wear or osteolysis was observed. The preoperative Merle d'Aubigne and Postel hip score increased from 11.6 to 17.1. CONCLUSIONS: Patients, who received third-generation CoC THA had no detectable wear and osteolysis. One ceramic fracture occurred, and the main reason for revision was dislocation.

Postoperative stability on lateral radiographs in the surgical treatment of pertrochanteric hip fractures.

BACKGROUND: Fixed-angle sliding hip-screw devices are commonly used to treat pertrochanteric fractures. The controlled impaction between the head and neck fragment and the femoral shaft fragment is crucial. However, the poor quality of fracture reduction can intercept controlled impaction and lead to excessive sliding. We hypothesized that excessive sliding occurs when most of the impaction is placed on the fragile posterior cortex of the fracture site. METHODS: This retrospective study included 128 AO/OTA type 31-A1 or 31-A2 fractures treated with fixed-angle sliding hip-screw devices. Cases involving reduced continuity of the anterior cortex at fracture site were defined as Type 1, those involving head and neck fragment anteriorly displaced relative to the femoral shaft fragment as Type 2, and those involving head and neck fragment posteriorly displaced relative to the femoral shaft fragment as Type 3. The extent of postoperative sliding distance of lag screw was measured. RESULTS: There were 52 cases of Type 1, 30 of Type 2, and 46 of Type 3, with no differences in patient characteristics between types. The mean ± standard deviation extent of sliding for types 1-3 was 4.5 ± 4.9 mm, 7.8 ± 5.6 mm, and 11.1 ± 6.0 mm, respectively (p < 0.0001). Sliding was significantly greater for Type 3 cases than for Type 1 or 2 (p < 0.0001 and p = 0.044, respectively). CONCLUSIONS: Excessive sliding occurs in surgical treatment for pertrochanteric fractures with posterior displacement of the head and neck fragment. In such cases, we recommend appropriate reduction prior to internal fixation.